Variable displacement pumps are known for their versatility of use in varying a displacement of fluid output therefrom. One type of variable displacement pump used in engines is a variable displacement gear pump. A conventional variable displacement gear pump may function to vary a displacement of fluid by the pump within its operating range. In some cases, a pressure relief valve may be provided at the output of the pump, to ensure the output pressure does not exceed a safe working pressure for the pump or downstream systems.
U.S. Pat. No. 8,899,951 discloses a variable displacement gear pump having a pump chamber and a regulating chamber. These chambers are separated from each other by a piston that is axially displacable according to a pressure differential between the pump and regulation chambers. One gear of the pump moves with the piston to vary the displacement of the pump.